Metal plating method and composition

ABSTRACT

FOR THE PURPOSE OF PLATING A METAL OBJECT WITH A PHOSPHORUS ALLOY, THE METAL OBJECT IS COATED WITH A MIXTURE IN FINELY DIVIDED FORM OF AN OXYGEN-CONTAINING PENTAVALENT PHOSPHORUS COMPOUND OF A METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBALT, IRON AND COPPER TOGETHER WITH AN ADDITIONAL QUANTITY IN SOME FORM OF AT LEAST ONE METAL OF THE GROUP.

United States Patent 3,582,387 METAL PLATING METHOD AND COMPOSITION Hoyt H. Todd, La Habra, Calif., assignor of fractional part interest to Jess M. Roberts, Ontario, Calif.

No Drawing. Continuation-impart of application Ser. No. 560,935, May 16, 1966, which is a continuation of application Ser. No. 311,075, Sept. 24, 1963, which is a continuation-in-part of applications Ser. No. 796,162, Feb. 27, 1959, and Ser. No. 156,986, Dec. 4, 1961, the latter being a continuation-in-part of applications Ser. No. 694,387, Nov. 4, 1957, and Ser. No. 765,715, Oct. 3, 1958, the latter being a continuation-in-part of application Ser. No. 694,389, Nov. 4, 1957. This application July 31, 1969, Ser. No. 846,618

Int. Cl. B44d 11/34 U.S. Cl. 117-22 18 Claims ABSTRACT OF THE DISCLOSURE For the purpose of plating a metal object with a phosphorus alloy, the metal object is coated with a mixture in finely divided form of an oxygen-containing pentavalent phosphorus compound of a metal selected from the group consisting of nickel, cobalt, iron and copper together with an additional quantity in some form of at least one metal of the group.

CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of my copending application filed May 16, 1966, Ser. No. 560,935, now abandoned, which is a continuation of my application Ser. No. 311,075 filed Sept. 24, 1963, and now abandoned, which is a continuation-in-part of application Ser. No. 796,162, filed Feb. 27, 1959, now abandoned, and Ser. No. 156,986 filed Dec. 4, 1961, now abandoned the latter being a continuation-in-part of my abandoned applications Ser. No. 694,387 entitled Method of Coating Metal With Phosphorus Alloy filed Nov. 4, 1957, and Ser. No. 765,715 entitled Wear Resistant Plating Method and Composition Therefor filed Oct. 3, 1958, the latter being a continuation-in-part of my abandoned application Ser. No. 694,389 of the same title filed Nov. 4, 1957.

BACKGROUND OF THE INVENTION This invention relates to a method of plating metal objects with phosphorus alloy coatings for various purposes, including corrosion resistance, oxidation-resistance, wear resistance and ornamentation.

The plating alloy may be nickel, cobalt or iron combined with phosphorus. Such a phosphorus alloy plating will fuse under heat to form a metallurgical bond with objects made of ferrous metals as well as objects made of cobalt, nickel, copper, silver, gold, palladium, and alloys of these metals.

The use of nickel-phosphorus platings is well known. The Crehan Patent 2,908,568, for example, discloses how a nickel-phosphorus alloy produced in advance of the plating operation may be placed on a metal object in finely divided state and then fused to the object by heat. The Horvitz Patent 2,633,631 discloses how such a nickelphosphorus alloy plating may be created on a metal object in situ by placing a mixture of nickel oxide and "ice ammonium phosphate on the object and then heating the object in a reducing atmosphere.

The phosphorus content of the final plating produced by the Horvitz process is less than 2%, whereas the desirable range of the phosphorus content is less than 10% but not less than 4%. Excellent results are produced when the phosphorus content is approximately 6%. If the phosphorus content is less than 4% the temperature requirement becomes excessive, the temperature varying inversely as the phosphorus content. If the phosphorus content is as low as even 3% the melting point is 2400 F. On the other hand if the phosphorus content is above the desirable range of 410%, the plating becomes porous, brittle and non-ductile. In addition, the high phosphorus content causes etching of the base metal with consequent dilution of the plating by the base metal.

Another disadvantage of the Horvitz process is that it is wasteful because a certain percentage of phosphorus is lost in the furnace, the phosphorus reacting with hydrogen to produce phosphine, a part of which is driven oil. It is a further disadvantage, of course, that the Horvitz process produces phosphine which is a serious hazard because phosphine is exceedingly poisonous. Another disadvantage of the Horvitz process is that if cobalt oxide is used without any other metal oxide, the cobalt oxide is not reduced satisfactorily.

. Another disadvantage of the Horvitz process is that the paint composition settles rapidly because the particles are excessively heavy, severe sedimentation occuring when the Horvitz mixture stands only ten minutes. Another disadvantage is that when the Horvitz paint composition is applied to a metal surface a long drying period is required because the drying time depends upon the evaporation of water. It is a further disadvantage that the Horvitz coating begins to deteriorate as soon as it dries, a white layer appearing on the surface of the dried coating and the dried coating being covered by a flowery bloom of recrystallized ammonia salt after a time period of forty-eight hours. A still further disadvantage is that the Horvitz composition has an etching effect on the base metal which dilutes the plating.

SUMMARY OF THE INVENTION A basic discovery is that a nickel-phosphorus coating or iron-phosphorus coating or copper-phosphorus coating or cobalt-phosphorus coating can be created in situ by applying to a metal body, a pentavalent phosphate of the nickel, cobalt, copper or iron and then heating the body in a reducing atmosphere. This discovery is surprising because phosphorus and phosphorus oxides vaporize or sublimate at relatively low temperatures and would be expected to do so instead of forming the plating alloys. Also phosphorus and the hydrogen present in most reducing atmospheres would be expected to combine to form phosphine.

This discovery eliminates the problem of releasing the poisonous gas phosphine. It employs simple, readily available materials that are inexpensive.

A second discovery is that any desired percentage of phosphorus in the final alloy in the desirable range of 4-10% can be obtained by adding nickel, cobalt, copper or iron to the pentavalent phosphate of nickel, cobalt, copper or iron.

Another discovery relates to the furnace temperature required for carrying out the plating operation. The earlier plating compositions set forth in the' above-mentioned copending applications all require a furnace temperature in the range of 1900-2100 F. (10381148 C.) to fuse the plating to a metal object, the temperature range being above the capability of the usual heat-treating furnace. After three years of research it was discovered that the required temperature could be reduced to 1700 F.

(927 C.) for a number of plating compositions by adding an alkali metal borate to the coating composition, lithium borate being preferred. Fortuitously the reduction in temperature made possible by the addition reduces grain growth in the metal plate and results in an exceptionally bright, smooth surface finish. The reduction in temperature is further desirable to reduce the tendency for the metal object to be warped by the heating operation.

The addition of small percentages of alkali metal halide to that of the alkali metal borates improves still further their wetting and fluxing action. The halide alkali metal salts exert a slight etching action on the base metal which aids the flow of the coating alloy by the capillary effect exerted by the roughened surface. The combination of alkali metal borates and halides is more effective than either by themselves as a menstrum agent for bringing about mutual solution of the coating ingredients.

Another discovery is that if particles of metal, for example, ferro-alloy particles, are brazed to a metal body by the nickel-phosphorus plate and then the heating operation is prolonged, the brazed particles completely dissolve and diffuse into the plate so as to modify its composition, the final coating having a smooth finish with no evidence of the added metal particles. Thus a given basic plating composition may be used to produce surface alloys of widely diiferent properties for different special purposes.

Another discovery is that any tendency for an alloy plating to crystallize may be met in many instances by adding a small amount of zinc to the plating composition.

Another discovery that is highly important for some purposes is that hard particles consisting of carbides of the transition metals may be added for incorporation in the plating composition to produce a surface that is highly wear resistant. A high percentage of amorphous tungsten carbide, for example, may be dissolved into the alloy plate in a surprising manner to result in an exceedingly hard plate containing crystallites of precipitated tungsten carbide.

Another discovery is that the addition of various amounts of tin up to about greatly increases the corrosion resistance of the alloy plating in all environments.

To carry out the process, the composition employed may be in the form of a finely divided dry mixture, the dry mixture being simply sprinkled on a metal body that is to be plated, the metal body then being heated to the required temperature in a reducing atmosphere. In the preferred practices of the invention, however, the finely divided material is suspended in a suitable vehicle to form a paint-like composition for application to the metal body before the heating step.

The paint-like coating composition has an indefinite shelf life, does not require continuous agitation, and dries very quickly. The process is highly flexible in the sense that ilt may be varied to result in various desired properties in the plating alloy. For example the melting point, the hardness, and the ductility of the alloy plate may be varied for specific needs. The phosphorus content may be varied by appropriate choice among the reducible salts, oxides and hydroxides of nickel, cobalt or iron to be mixed with the pentavalent phosphate of nickel, cobalt, iron or copper.

The pentavalent phosphate of nickel, cobalt, iron or copper may be produced as an initial part of the process, commercial phosphoric acid, which consists primarily of ortho-phosphoric acid (H PO may be used conveniently and economically, the result being orthophosphates of nickel, iron or cobalt. For example, combining nickel carbonates and phosphoric acid results in the reaction Each unit of NiCO requires 0.647 unit of commercial H PO for completion of the reaction.

It has been discovered that, if phosphoric acid in excess of the above amount is used and the furnace atmosphere contains a substantial amount of oxidizing gases such as CO and H 0, compound of nickel, phosphorus and oxygen evaporates at a temperature in the neighborhood of 1500 F. and condenses in the cooler portions of the furnace as a brownish yellow powder. If there is no excess of phosphorus in the coating material, i.e., if the phosphorus content does not exceed the stoichiometric quantity for Ni 1(P0 the process may be carried out at temperatures well above 1600 F. with no appreciable loss of either phosphorus or nickel.

If only Ni (PO or the equivalent quantities of nickel and phosphorus are used in the paint composition that is applied to a ferrous metal object, a nickel-phosphorus alloy plate will form in the reducing atmosphere at a high temperature but the alloy plating will not be suitable for corrosion resistance because of its high percentage of phosphorus. The phosphorus content will be on the order of 20%, far in excess of the desirable range of 4-10%. The high phosphorus content of the plating results in porosity. The high phosphorus content, moreover, causes etching of the base metal with consequent dilution of the plating by the base metal. In addition the plating is brittle and nonductile so that dimensional changes during cooling causes micro cracking in the plating.

It is for these reasons that some form of one of the four metals is added to the coating composition to reduce the proportion of phosphorus in the plating. The added metal may be in the form of pure metal or may be an ingredient of a compound that is reducible in a hydrogen atmosphere in the range of 1700-2000 F. Thus the reducible compound may be an oxide of the metal, or a salt of the metal or a hydroxide of the metal.

Ordinary hydrous nickel phosphate is not operative for the purpose of the invention because the applied paint composition blisters and peels. It was finally discovered that these difficulties could be traced to the water content of the phosphate which amounts to about 25%. It was further found that the water content causes coagulation and caking in the inorganic suspensions. Thorough dehydration of the phosphate eliminates these difficulties, and in addition eliminates the gummy character that makes it hard to grind the phosphate. Dehydration may be accomplished by heating the hydrated phosphate for 2 to 3 hours in the temperature range of 265300 F. in open air.

Complete dehydration changes the color of nickel phosphate from light green to yellowish brown and it thereafter resists hydration even if left in water for a long period. The dehydrated phosphate may easily be ground to a fine degree of subdivision in an organic solvent. One hundred grams of nickel carbonate containing 49.5% nickel reacts with 64.7 grams of 85% H PO to produce hydrated nickel phosphate, which after dehydration weighs approximately 103 grams. Since the dehydrated phosphate contains 48% nickel by weight and 16.9% phosphorus, it is a simple matter to calculate the amount of metal that must be added to the composition to reduce the phosphorus content to any desired point in the range of 4-l0%.

An ideal binder is the previously mentioned hydrocarbon soluble acrylic resin which may be purchased in powder form or as a thick syrup. This material sublimes off in the furnace. From 7.5 to 10% dry weight of the resin is dissolved in a mineral spirit having a boiling point in the neighborhood of 180280 F. The boiling point may be varied to suit particular applications.

An alcohol is added to provide two immiscible liquids and the two liquids are emulsified with the aid of an emulsifying agent, which agent may be the oil-soluble oxy-ethylated-alkylphenyl compound. It is this emulsion which solves the problem of sedimentation and caking of the coating composition.

Various fluxing agents may be added within the skill expected in this art.

It has been found that an alkali metal borate may be added to lower the temperature at which the plating melts and to produce a smooth plate by its dissolving action on the various components of the coating composition. Superior results are obtained with lithium borate. Lithium tetra-borate is preferred and, as heretofore noted, must be in the anhydrous state to keep the plating composition from peeling during heating.

It is apparent that the anhydrous alkali metal borate is not merely a fiuxing agent since it serves as a common menstrum in which all of the constituents of the coating composition are partially soluble and thus brings the constituents into intimate contact with each other to make a more homogeneous composition. The surface tension effect of the alkali metal borate accounts for the smoothing out of the plate. The presence of the alkali metal borate further aids in the reduction of such oxides as those of chromium and manganese.

DESCRIPTION OF THE PREFERRED PRACTICES OF THE INVENTION As heretofore stated, to obtain a phosphorus alloy plating in which the phosphorus content is in the desired range of 410%, it is necessary to add metal from the selected group of metals and the metal may be either in the form of a pure metal or in the form of one of the heretofore mentioned compounds of the metal.

Some of the following examples use a ready made pentavalent phosphate of a selected metal, for example, nickel phosphate. Other examples include a preliminary step of producing such a pentavalent phosphate by the reaction of a phosphorus compound with a compound of the selected metal. It is to be understood that either procedure may be substituted for the other in each of the examples.

In each example, what may be termed a pigment consisting of the pentavalent phosphate of the selected metal plus additional metal plus a compound of an additional metal blended therewith is mixed with three additional materials and ground to a size range of 1-5 microns. The three additional materials are a solution of hydrocarton soluble acrylic resin in mineral spirits, oil soluble oxy-ethylated-alkyl-phenyl compound, an anhydrous lithium tetra-borate. After the grinding operation, an alcohol is added and the mixture is well shaken or otherwise agitated to produce an emulsion which is the desired paintlike composition for use in coating metal objects. It being understood that this procedure if followed, it is sufficient for each example merely to give the quantities to be used of the various materials.

Example 1 To produce 10 pounds of pigment, 2152.8 grams basic nickel carbonate is thoroughly mixed with 3991.9 grams nickelous oxide (NiO) and then stirred into 3000 cc. of water. 1393 grams of 85% commercial ortho-phosphoric acid is then stirred into the mixture. After the reaction ceases, the phosphate mixture slowly hydrates to a solid cake. The reacted cake is then dried in an oven at approximately 300" F. until dehydrated.

As heretofore indicated the same pigment may be produced simply by mixing the calculated quantity of anhydrous nickel phosphate with the nickel oxide. The addition of the nickelous oxide before the reaction, however, instead of after the reaction, is advantageous because it produces a more intimate mixture of the phosphate 6 and the oxide. A further advantage is that this procedure saves time.

For grinding to fine size, 4 pounds of this pigment is mixed with 15 grams of anhydrous lithium tetra-borate, 1 gram lithium chloride and 1 gram sodium chloride, 25 cc. of oil soluble oxyethylated-alkyl-phenyl compound and 1100 cc. of the 10% by weight solution of acrylic resin in mineral spirits. After the grinding operation 50 cc. of isopropanol is added with agitation to produce the final emulsion which is a paint-like suspension.

When the paint-like mixture is applied to a metal object and the metal object is heated in a reducing atmosphere to approximately 1700 F., an alloy plating is produced that contains 8%% phosphorus.

Example 2 Example 3 The pigment consists of three well blended materials:

33 grams anhydrous nickel phosphate analyzing 36% nickel and 12.1% phosphorus 106.5 grams NiO analyzing 79% nickel 0.75 gram ZnO For the grinding operation the pigment is mixed with the following:

1 gram anhydrous lithium tetra-borate 0.1 gram lithium chloride 0.1 gram sodium chloride 1 cc. oxy-ethylated-alkyl-phenyl compound 60 cc. 10% acrylic resin solution After grinding to a fine particle size, preferably 1-2 microns, 1 cc. ethyl alcohol is added with agitation to produce the final emulsion.

In a reducing atmosphere of hydrogen the coating composition fuses to an alloy plating at 1700-" F. The alloy contains 95.5% nickel, 4% phosphorus and 0.5% zinc. The presence of the small quantity of zinc prevents the formation of crystallites in the coating during solidification.

Example 4 To produce the pigment, iron phosphate is prepared by reacting 100 grms of carbonyl iron powder with 137 grams of orthophosphoric acid and the product of the reaction is dried at 300 F. The reaction product contains 46.7% iron and 17% phosphorus. To complete the pigment 47 grams of the dried reaction product is mixed with 123 grams iron oxide containing 43% iron.

For the grinding operation this pigment is mixed with 2 grams anhydrous lithium tetra-borate 0.2 gram lithium chloride 0.2 gram sodium chloride 2 cc. oil soluble oxy-ethylated-alkyl-phenyl compound 300 cc. 10% acrylic resin solution After the grinding operation, 10 cc. ethyl alcohol is added with agitation to produce the final emulsion.

A coating of the paint-like composition on a metal object fuses at 2000 F. in a hydrogen atmosphere to produce an alloy plating containing 92% iron and 8% phosphorus.

Example 5 To produce a pigment, 100 grams CoCO is reacted with 64 grams H PO (85% strength) in accordance with the following reaction:

The cobalt phosphate is then dried to an anhydrous state by heating to 300 F. For the grinding operation the above pigment is mixed withthe following:

175 grams cobalt oxide C 0 5 grams anhydrous lithium tetra-borate 0.5 gram lithium chloride 2 cc. oxy-ethylated-alkyl-phenyl compound 150 cc. solution of acrylic resin After the grinding operation 7.5 cc. ethyl alcohol is added with agitation to produce the final emulsion. The paintlike composition fuses at 2000 F. in a hydrogen atmosphere to produce an alloy plating of cobalt and phosphorus.

Example 6 50.5 grams basic copper carbonate 79.0 grams copper oxide (CuO) Mix Well.

Add 20 cc. H 0 and 29.8 grams of 85% H PO Allow to react. Dry the reacted products at approximately 300 F. until free of moisture.

Add 1 gram lithium tetra-borate and .1 gram LiCl and .1 gram NaCl.

Add 100 cc. 10% acrylic resin vehicle. After the mixture is ground to 3-5 micron particle size, 2 cc. of ethyl alcohol is added with agitation to produce the final emulsion. The coating fuses in a hydrogen atmosphere at 1700 F.

Example 7 This example involves diffusion and for this purpose the high temperature is maintained for several minutes after the paint-like composition fuses. The purpose of continuing the heating operation is to permit homogenization by diffusion of the alloying elements. In some instances the diffusion is the diffusion of a solid or a melted solid and in other instances gaseous diffusion is involved. The added material dissolves into the nickel phosphorus alloy during the added heating period to result in a high concentration of localized depth of the added material.

The pigment for the present example is a mixture of the following:

41.6 grams anhydrous nickel phosphate analyzing 36% nickel and 12.1% phosphorus 30 grams low carbon fen'ochrome powder (200 mesh) analyzing 66% chromium, 5% silicon and the balance iron 51 grams nickel flake (-100 mesh) For the grinding operation the pigment is mixed with the following:

9 grams anhydrous lithium tetraborate 0.5 gram lithium chloride 0.5 gram sodium chloride 1 cc. oil soluble oxy-ethylated-alkyl-phenyl compound 100 cc. 10% acrylic resin solution After the mixture is ground to a particle size of 5-10 microns, 2 cc. of ethyl alcohol is added with agitation to produce the final emulsion.

A coating of the composition on a clean ferrous metal surface fuses to a nonporous plating in hydrogen at 1900 F. The fused coating is held at the elevated temperature for to 30 minutes to carry out the diffusion process.

Example 8 The pigment is a mixture of 80 grams tungsten carbide (6% carbon) of a particles size of 1-2 microns and 41.6

grams anydrous nickel phosphate analyzing 36% nickel and 12.1% phosphorus. For the grinding operation the pigment is mixed with the following:

2 grams anhydrous lithium tetraborate 0.1 gram lithium chloride 0.1 gram sodium chloride 1 cc. oxy-ethylated-alkyl-phenyl compound 55 cc. 10% acrylic resin solution After the grinding operation 2 cc. of ethyl alcohol is added with agitation to result in the final emulsion. Preferably the mixture is ground to a particle size of 1-2 microns.

The composition fuses into an alloy plating in a hydrogen atmosphere at 2000 F. The tungsten carbide dissolves in the nickel matrix and reprecipita-tes upon cooling as small crystallites. The plating contains tungsten carbide, the analysis being 75.2% tungsten, 15% nickel, 5% phosphorus and 4.8% carbon.

The inclusion of only 1% of tin in the phosphorus alloy results in excellent oxidation resistance; the inclusion of 5% of tin results in optimum corrosion resistance for general application; the inclusion of 10% of tin produces maximum corrosion resistance in sea water. The following tin.

Example 9 To produce an alloy of nickel, 4% phosphorus, and 1% tin, use:

33.4 grams anhydrous nickel phosphate (analyzing 35 Ni and 12% P) 1.5 grams stannous oxide (SnO) 106 grams nickel oxide (NiO) cc. of a vehicle consisting of 20% by weight of acrylic resin dissolved in naphtha Example 10 To produce an alloy of 87% nickel, 8% phosphorus and 5% tin, use:

66.7 grams anhydrous nickel phosphate (analyzing 35% Ni and 12% P) 5.66 grams stannous oxide (SnO) 81.5 grams nickel oxide (NiO) 100 cc. of the above vehicle Example 11 To produce an alloy of 83 nickel, 7% phosphorus and 10% tin, use:

58.5 grams anhydrous nickel phosphate (analyzing 35 Ni and 12% P) 78.5 grams nickel oxide (NiO) 11.3 grams stannous oxide (SnO) 100 cc. of the above vehicle In these Examples 9, 10 and 11, the solid material should be ground to a particle size of 0.5 to 1.0 micron. The composition in Example 9 fuses at 1800 F. in hydrogen and the composition in the last two examples fuse at 1700 F.

Example 12 After grinding the mixture to a particle size of 1-5 micron, 1 cc. of ethyl alcohol is added with agitation and then 50 to 80 grams of finely divided tungsten carbide is mixed in for the production of the final emulsion.

three examples give these three different proportions of This example demonstrates the advantage of employing alkali metal borate alone or alkali metal borate together with an alkali metal halide in the procedure of forming a nickel-phosphorus plating in accord with the teaching of the Crehan patent wherein the nickel-phosphorus alloy is produced in advance and then finely divided for application.

' Example 13 100 grams nickelous oxide (NiO) 40 grams monoammonium phosphate ((NH )H PO 50 cc. H

5 grams anhydrous lithium tetraborate 1 gram lithium chloride 320 grams finely divided tungsten carbide This mixture is brushed on the surface of a metal body that is to be plated and is allowed to become reasonably dry. The coated metal body is then heated in a reducing atmosphere, such as hydrogen, to produce the desired nickel ,plate with the nickel plate fused to the base metal. This eiiample demonstrates the advantage of adding alkali metal borate alone or alkali metal borate plus an alkali metal halide to a plating composition in accord with the teaching of the previously mentioned Horvitz patent.

This example also demonstrates the unexpected fact that the nickel-phosphorus alloy produced in accord with the teaching of the Horvitz patent may contain dissolved tungsten carbide up to 80%.

My description in specific detail of selected practices of the invention will suggest various changes, substitutions and other departures from my disclosure.

I claim:

1. A method of plating a metal body, including the steps of:

forming an initial composition consisting essentially of the constituents in finely divided form of a phosphorus alloy of a metal selected from the group consisting of nickel, cobalt, iron and copper;

mixing finely divided tungsten carbide with said composition;

applying the resulting composition to the surface of the body; and

heating the body and the applied material thereon in a reducing atmosphere to cause plating of the body with the phosphorus alloy that is formed by said constituents with the tungsten carbide dissolved into the alloy.

2. A method as set forth in claim 1 in which the initial composition is essentially a pentavalent phosphate of a metal selected from the group consisting of nickel, cobalt, iron and copper.

3. A method as set forth in claim 1 in which the initial composition consists essentially of an oxide of the selected metal and an ammonium-containing phosphorus compound.

4. A method as set forth in claim 1 in which said initial composition consists essentially of a finely divided phosphorus alloy of the selected metal.

5. A method as set forth in claim 1 inwhich the initial composition consists essentially of an oxide of the selected metal and monoammonium phosphate.

6. A method of forming a metallurgically bonded plating on a metal body wherein the plating comprises phosphorus and metal selected from the group consisting of nickel, cobalt, iron and copper, the percentage of phosphorus in the plating being within the range of 4 to by weight of the plating which is less than the percentage of phosphorus in a given pentavalent phosphate of a metal selected from said group, comprising the steps of:

applying to the surface of the metal body a coating consisting essentially of a mixture of said pentavalent phosphate of the selected metal and an additional quantity of metal selected from said group present either in the form of pure metal or in the form of an ingredient of a compound that is reducible in a hydrogen atmosphere in the temperature range of 1700- 2000 F.,

the amount of the additional metal being sufficient to make the percentage of phosphorus in the final plating within the range of 4 to 10% by weight of the plating; and

heating the metal body with the coating thereon in a reducing atmosphere to cause the coating to form a. phosphorus alloy of metal selected from said group.

7. A method as set forth in claim 6 in which said mixture constitutes at least by weight of the coating.

8. A method as set forth in claim 6 which includes the addition of low carbon ferrochrome in finely divided form and in which the heating step is continued after the phosphorus alloy forms to result in diffusion of the low carbon ferrochrome into the alloy.

9. A method as set forth in claim 6 in which the coating includes at least one alkali metal compound selected from the group consisting of alkali metal borate and alkali metal halides for wetting and fluxing action, to serve as a menstrum agent for bringing about mutual solution of the coating ingredients and to reduce the temperature to which the metal body must be heated to form the phosphorus alloy.

10. A method as set forth in claim 6 in which said coating includes some form of tin to make up 1 to 10% of the weight of the plating.

11. A method as set forth in claim 6 in which some form of zinc is added to said coating as a deoxidizer and to increase the wetting action of the coating and to prevent the formation of crystallites luring the solidification of the plating.

12. A method as set forth in claim 6 in which said mixture consists of finely divided particles and said coating is in the form of a liquid suspension of the finely divided particles.

13. A method as set forth in claim 6 in which said coating comprises the finely divided mixture in dry form.

14. A composition for application to a metal body to produce an alloy metallurgically bonded thereto upon the heating of the metal body in a reducing atmosphere, wherein the alloy comprises phosphorus and metal selected from the group consisting of nickel, cobalt, iron and the amount of the additional metal in the mixture being sufficient so that the amount of phosphorus present in the mixture is within the range of 4 to 10% by weight of the total amount of phosphorus and metal present.

15. A composition as set forth in claim 14 in which the composition is in the form of a paint-like liquid suspension of finely divided particles, said mixture comprising at least 80% by weight of the solids of the composition.

16. A composition as set forth in claim 14 which includes at least one alkali metal compound selected from the group consisting of alkali metal borate and alkali metal halides.

17. A composition as set forth in claim 14 which includes some form of tin to make up 1 to 10% of the weight of the alloy.

18. A composition as set forth in claim 14 which includes some form of zinc to function as a deoxidizer and to increase a wetting action and to prevent the formation of crystallites during a solidfication of the alloy.

(References on following page) References Cited UNITED STATES PATENTS Chodwick 148--6.15

Coslett 148-6.15X

Flanzer et a1. 117229X Claus 75-17 Jerabek 11722X Alexander 117130X Horvitz 29196 Diffenderfer 117130X Mitchell et a1 11722X 12 2,766,138 10/1956 Talmey 117130X 2,930,521 3/1960 Koehring 230-133 OTHER REFERENCES 5 Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 8, 1925, pp. 833, 834, and 860.

WILLIAM D. MARTIN, Primary Examiner 10 E. J. CABIC, Assistant Examiner US. Cl. XJR. 

